Adaptive Dose Painting by Numbers for Head-and-neck Cancer

Purpose: To investigate the feasibility of adaptive intensity-modulated radiation therapy (IMRT) using dose painting by numbers (DPBN) for head-and-neck cancer.

Methods And Materials: Each patient's treatment used three separate treatment plans: fractions 1-10 used a DPBN ([(18)-F]fluoro-2-deoxy-D-glucose positron emission tomography [(18)F-FDG-PET]) voxel intensity-based IMRT plan based on a pretreatment (18)F-FDG-PET/computed tomography (CT) scan; fractions 11-20 used a DPBN plan based on a (18)F-FDG-PET/CT scan acquired after the eighth fraction; and fractions 21-32 used a conventional (uniform dose) IMRT plan. In a Phase I trial, two dose prescription levels were tested: a median dose of 80.9 Gy to the high-dose clinical target volume (CTV(high_dose)) (dose level I) and a median dose of 85.9 Gy to the gross tumor volume (GTV) (dose level II). Between February 2007 and August 2009, 7 patients at dose level I and 14 patients at dose level II were enrolled.

Results: All patients finished treatment without a break, and no Grade 4 acute toxicity was observed. Treatment adaptation (i.e., plans based on the second (18)F-FDG-PET/CT scan) reduced the volumes for the GTV (41%, p = 0.01), CTV(high_dose) (18%, p = 0.01), high-dose planning target volume (14%, p = 0.02), and parotids (9-12%, p < 0.05). Because the GTV was much smaller than the CTV(high_dose) and target adaptation, further dose escalation at dose level II resulted in less severe toxicity than that observed at dose level I.

Conclusion: To our knowledge, this represents the first clinical study that combines adaptive treatments with dose painting by numbers. Treatment as described above is feasible.